There are several issued patents dealing with the use of test patches in xerographic marking systems. Two of these are Xerox U.S. Pat. Nos. 7,418,216B2 and 7,224,919B1. The disclosures of these patents are incorporated by reference into the present disclosure.
It is common practice in some xerographic marking systems to use test patches to monitor certain parameters of the process such as developer density, print quality, etc. The test patches are usually positioned between predetermined customer image areas called “gaps”. It is generally the case that test patches which can be developed latent images are never transferred to a receiving medium like paper but rather, after developed, the developed image is tested for image density or any other quality desired. Once the desired tests are conducted on the test patches, the patches are rotated on the photoconductive belt to a cleaning station where the toner or developer is removed leaving this space or gap available for future test patches. Many times it requires several belt revolutions through the cleaning station to effectively remove all of the developer.
The test patches before removal are sensed by various sensors and monitors to measure for the properties desired in the marking system. Once these desired properties are measured, the marking system can be tweaked for any adjustments that need to be made, for example, to the toner and developer to reach the desired final toner density. The image on the test patches, as above indicated, are rarely transferred to a receiving medium because the desired measurements can be readily made directly only from the patch developed image.
Generally, a “patch” can be defined as a rectangular or other shaped area on the belt that is used for monitoring process control. These patches are usually printed between the customer image areas, also referred to as “image panels”. Patches are used to control image quality. In some cases, a patch is an area of charge that is not developed. That area is read by the Electrostatic Voltmeter (ESV). Patches used to determine and control toner concentration are read by optical sensors and monitors before adjustments are made. The patches are placed in positions similar to the positions or “gaps” above defined. The control patches are sensed with any suitable sensors, such as ESV and ETAC sensors and, based on the reads, adjustments are made to the toner density, belt charge and other xerographic components to achieve the customer's desired print quality output.
Usually a test patch test is conducted when software customers make requests to use space on the belt to position these images (patch). Availability of space on the belt is based on questions such as: do we have time to print this image and is there space on the belt that has not already been used? The customer's request will then be scheduled once determinations have been made results forwarded to the customer.
Under the prior art approaches prior to the implementation of the algorithm presently defined in this invention, when a patch request is received, the time of the start of the seam zone of the next forward or normal belt revolution is checked against the time necessary for patch transfer to determine if the patch request could be allocated at that time. This causes a problem because there are many cases where unsearched panels in a previous normal belt revolution could have been used to schedule the patch request. However, because of the scheduling algorithm in use, patches are being scheduled on average usually 1100 milliseconds later than actually possible based on availability of space at the time of request.